Spring themes allow end users to dynamically change look and feel.
From a design/ architecture point of view all the theme is, is a static group of resources such as stylesheet, images etc.
Multiple themese can be configured and then the user can switch between by simple passing a desginated parameter (usually "theme") in a servlet request.
For demo see here: http://viralpatel.net/blogs/2010/10/spring-3-mvc-themes-tutorial-example.html
Just wondering what would be the closest JSF has to match this feature? Or how would you do it in JSF?